Bordetella parapertussis is a small Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 bacterium of the genus Bordetella

Bordetella

Bordetella is a genus of small , Gram-negative coccobacilli of the phylum proteobacteria. Bordetella species, with the exception of B. petrii, are obligate aerobes as well as highly fastidious, or difficult to culture. Three species are human pathogens ; one of these Bordetella is a genus of small...

which is adapted to colonise the mammalian respiratory tract. Pertussis caused by B. parapertussis manifests with similar symptoms to B. pertussis

Bordetella pertussis

Bordetella pertussis is a Gram-negative, aerobic coccobacillus of the genus Bordetella, and the causative agent of pertussis or whooping cough. Unlike B. bronchiseptica, B. pertussis is non-motile. Its virulence factors include pertussis toxin, filamentous hæmagglutinin, pertactin, fimbria, and...

-derived disease but tends to be generally less severe. Immunity derived from B. pertussis does not protect against infection by B. parapertussis, however, because of the O-antigen that is found only on B. parapertussis. This antigen protects B. parapertussis against antibodies specific to B. pertussis, so the bacteria is free to colonize the hosts lungs without being subject to attack by previous antibodies. These findings suggest that B. parapertussis evolved in a host population that had already developed immunity to B. pertussis, where being able to evade B. pertussis immunity was an advantage.

Two lineages of B. parapertussis have been described. The first infects humans and is responsible for a minority of cases of the disease pertussis

Pertussis

Pertussis, also known as whooping cough , is a highly contagious bacterial disease caused by Bordetella pertussis. Symptoms are initially mild, and then develop into severe coughing fits, which produce the namesake high-pitched "whoop" sound in infected babies and children when they inhale air...

 (also known as whooping cough). The second, ovine, lineage causes chronic non-progressive pneumonia

Pneumonia

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

 in sheep. Both lineages are thought to have evolved from a B. bronchiseptica

Bordetella bronchiseptica

Bordetella bronchiseptica is a small, gram-negative, rod-shaped bacterium of the genus Bordetella. It can cause infectious bronchitis, but rarely infects humans. Closely related to B. pertussis—the obligate human pathogen that causes pertussis or whooping cough—B...

-like ancestor. This disease can be symptomatic or asymptomatic and may predispose hosts to secondary infection.